Project Summary/Abstract HIV-infected youth age 15 – 24 in sub-Saharan Africa are not experiencing the same gains in quality of life and improved life expectancy from antiretroviral therapy (ART) as older adults, largely due to lower retention in care and viral suppression. Leveraging the social networks of HIV-infected youth to improve engagement in ART care may be an efficient and durable way to improve treatment outcomes, however little is known about social networks of youth or the influence of social networks on HIV treatment outcomes in resource-limited settings. Through specific training and structured mentorship I will investigate the role social networks play in retention in care and viral suppression among youth in this mentored career development award. I will use cross- sectional analysis of existing social network data collected as part of a large, population-based test-and-treat trial as well as new, longitudinal data on the social networks of youth who seroconvert during follow-up and use the results to inform the design and implementation of a network-based intervention to improve HIV treatment outcomes among youth. My research aims are: (1) Evaluate the influence of social network attributes on retention in care and viral suppression among youth (15 – 24 years) in western Kenya; (2) Investigate longitudinal changes in the social networks of youth before and after HIV diagnosis; and (3) Design and pilot a network-based intervention to improve retention in care and viral suppression among HIV-infected youth based on results from Aim 1 and Aim 2. I will leverage the research infrastructure and sociometric social network data on over 52,000 community members including 17,069 youth age 15 – 24 in 12 communities in rural Western Kenya collected at baseline during the ongoing SEARCH (NCT01864603) test-and-treat trial. I will accomplish my training aims through coursework, workshops, and guidance from mentors who are experts in social network analysis, advanced epidemiologic methods, youth in East Africa, HIV treatment strategies, and intervention development. My training aims are: (1) Develop expertise in the theory and analysis of social network data and apply social network analysis to understand HIV treatment outcomes; (2) Gain experience in network data collection; (3) Apply advanced longitudinal analysis methods to network data; and, (4) Gain experience using network data to inform intervention development. The rigorous training in social network theory and methods, intervention development, and the interdisciplinary mentorship team committed to my success will position me as an independent physician-scientist with network expertise in the HIV treatment field. The data generated from this K23 will inform the development of an R01 that will evaluate the effectiveness of a social network based intervention to improve clinical outcomes among HIV-infected youth in East Africa in a cluster-randomized control trial.